1. Field of the Invention
The present invention relates to sheet processing and rewinding devices, and, more particularly, to a machine for separating double-rolled thin aluminum sheet into two single-thickness sheets which are wound onto separate winding shafts, under controlled conditions, using motors of variable speed and torque to control the supply, advancement, and winding of the sheet at a controlled speed and sheet tension.
2. Description of the Prior Art
It has become common practice to produce thin aluminum sheet or aluminum foil in a double-rolled form which requires the subsequent separation of the double-sheet into two separate sheets, preferably in combination with the longitudinal slitting of the sheet into a plurality of sheet strips. In known sheet processing machines used for this purpose, the base parameter for the sheet drive is a constant sheet speed in the processing section of the machine, determined by a variable-speed motor which drives the traction rolls and deflecting rolls of the processing section. Included with the latter may be appropriate separating rolls and sheet slitting means. The sheet speed is monitored by means of a sheet speed measuring device, for example, a tacho-generator. It follows that the drive parameters for the supply shaft are predetermined by the preset sheet speed, taking also into account the decreasing diameter of the supply coil.
A known machine of the aforementioned type features means for measuring the sheet tension between the supply coil and the processing section of the machine, utilizing this measurement to control the torque of the motor-generator of the supply shaft drive to maintain a constant sheet tension. This kind of control system requires expensive drive components, considering the necessary high power output ratings, And, in spite of the use of very powerful drive components, such a machine tends to encounter problems of inaccurate control during the startup and acceleration phase of its operation, in view of the large mass which needs to be accelerated, when the supply shaft carries a full coil. The drive controls also must provide a continuous adjustment of the supply shaft drive to the decreasing supply coil diameter.
The aforementioned shortcomings of the known sheet processing machine represent basic difficulties which are inherent with this type of control system. The drive motors for the winding shafts have control means which maintain a constant sheet winding tension. No major problems are encountered with these winding devices.